Hypothesis: Protein catabolism & synthesis & their relative rates are influenced by therapeutic interventions in children with renal insufficiency. Primary aim of study: Assess the impact of rhGH therapy on protein & energy metabolism in CRF or ESRD via 2 established stable isotope methods. Hypothesis: Urea nitrogen appearance is inadequate for estimation of net protein catabolism. Secondary aim of study: Measure urea nitrogen excretion simultaneously c/above tracer methods, & determine the relationship c/these methodologies.